This invention relates to a film (sometimes called "plastic sheet") folding device for a film winding machine, film slitter, film bag manufacturing machine, etc. and more particularly, this invention relates to a device for folding thin film which is running one direction, in U shape or C shape in cross section along a longitudinal line.
In one prior device, as shown in FIG. 10, film 2 (sometimes called plastic sheet) is fed in an inclined upward direction from feed roller 1, folding roller 3 is inserted at reverse side of film 2 at folding line 2a, and folding bar 5 is provided above the folding roller 3 for folding outer part 2b along folding line 2a on the reverse side of folding plate 4. Roller 6 is a secondary feeding roller. If the end 3a of folding roller 3 were a point, the folding would be performed precisely, however, the tensile force of the film is concentrated at point 3a, and can cause an injury and resulting rupture. For avoiding the concentration of tensile force, the configuration of the end 3a should be a sphere or a similar shape to a sphere. In practice, however, it causes an error in folding and the concentration of the tensile force can not be avoided perfectly. The error of folding is modified at the edge 4a of the folding plate 4, however, the part of the film folded by the end 3a of a folding roller 3 remains, and the remaining folded part disappears in the case of resilient film such as polyethylene film. However, in the case of less resilient film such as stretched polypropylene film (DPP) or cast polypropylene film (CPP), or paper, the remaining folded part becomes permanently creased 1c, 1c, . . . and harms appearance.
For avoiding said concentration of tensile force on the film, there is an apparatus for folding film by triangle plate.
FIG. 11 shows a prior art half folding device using a triangle plate, in which film 2 is fed to a triangle plate 7, the folded film 2x at the under part of triangle plate 7 being fed in a lateral direction. However, this widens the occupying area of the apparatus because the delivering direction of the film 2 must make a right angle to the feeding direction of the film 2. Moreover in the case of film of uneven thickness, it is difficult to adjust the angle of triangle plate 7 which is necessary to prevent the production of a crease in film. When the film to be folded in half is substituted for a half size film 8 in width such as inflation film in a prior device as shown in FIG. 12, film 8 runs at an inclined edge to triangle plate 7, making it useless to try to prevent a crease in the film. Moreover, if the film 8 slips at the inclined edge of triangle plate by the length e.sub.1, the position of delivering film 8 is offset by the length d.sub.1, and such a variation of the position of the film 8 produces an error in the operation of a photo electrical film detecting device hole punch, gusset insertion device, slitter etc. in a bag manufacturing device of a slitter etc.